Implement Cast Streaming mirroring, DLNA casting, daemon+GUI, and breadd integration

Builds out the full v1 scope: a vendored+patched openscreen subset for
low-latency Cast Streaming (Mirroring receiver 0F5096E8) alongside the
existing Cast V2/HLS and new DLNA/AVTransport casting paths, breadcastd's
Idle/Casting state machine with a private IPC socket, the breadcast GTK4
popup as a thin IPC client, and bread.cast.*/bread.command.cast.* breadd
integration (device discovery, start/stop, mirroring lifecycle events).
Also adds bakery/systemd/Forgejo CI packaging.

Validated end-to-end against a real Chromecast/Google TV: negotiated
Cast Streaming session, live pipeline playback, and daemon+GUI click-to-cast/
stop through the actual popup.

.gitignore

@@ -0,0 +1,34 @@
+# Rust build artifacts
+target/
+
+# Editor and IDE files
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+
+# OS artifacts
+.DS_Store
+Thumbs.db
+desktop.ini
+
+# Environment and secrets
+.env
+.env.*
+*.env
+*.pem
+*.key
+*.p12
+secrets/
+
+# Log files
+*.log
+logs/
+
+# Runtime files
+*.sock
+*.pid
+
+# Local hygiene notes (not for commit)
+CLAUDE.md